For example, Japanese Patent Application Laid-Open Publication No. 2011-91477 (Patent Document 1) describes a method of synchronizing a plurality of forwarding databases (FDBs) with each other in a chassis-type switching hub. More specifically, each of line cards generates a learning-use frame when a registered content of each FDB is changed, and the learning-use frame is transmitted toward the other line card while a transmission rate is controlled. Japanese Patent Application Laid-Open Publication No. 2012-209855 (Patent Document 2) describes a method of effectively learning the FDB in the chassis-type switching hub. More specifically, a representative line card is determined, and each line card enables the representative line card to perform a learning process based on a learning notification when the FDB information of a received packet has not been learned yet, and then, the FDB of its own is updated based on a learning notification transmitted in multicast transmission from the representative line card. The representative line card limits a flow rate in the multicast transmission.
In a frame relay device that divides the same VLAN into two subnets for management, Japanese Patent Application Laid-Open Publication No. 2012-130084 (Patent Document 3) describes a method of distinguishing a communication inside the same subnet from a communication between the subnets. More specifically, if flooding occurs for the frame received at a first domain processing unit corresponding to a first subnet, a learning table of the first domain processing unit learns a transmission-source address of the frame together with a flag “0”, and a learning table of a second domain processing unit corresponding to a second subnet learns the transmission-source address together with a flag “1”. When an address is retrieved, it is distinguished whether the transmission address is inside the same subnet or not, by a value of the flag. Also, the frame relay device limits a band in communication between the subnets.